1. Field of the Invention
The present invention relates to a color separator, especially to a time-sequential color separator and a liquid crystal projector including the color separator.
2. Description of the Related Art
Conventional color separators are normally classified into mechanical type and electronic type. The former uses various color filters to mechanically separate color lights from an incident white light. Such a mechanical type color separator normally has a complex structure, a big volume and all of the drawbacks due to mechanical movement. The latter is constructed by electronic circuits and light valves. Therefore the quality of an electronic type color separator is related to the response speed of light valve, the transmittance, the color purity and the contrast ratio.
A conventional electronic type color separator as disclosed in U.S. Pat. No. 4,232,948 by Shanks uses a liquid crystal light valve, which can change the polarization of a light passing therethrough, and a retarder having a birefringence effect to change the observed color of the light passing through the device. The transmittance, the switching speed and the color purity obtained by such a color separator is not desirable. Furthermore, in U.S. Pat. No. 5,347,378, Handschy et al. utilize a structure which combines a color-selective filter with a fast-switching liquid crystal light valve. However, the transmittance and the color purity obtained by the color separator are still not satisfactory.
Accordingly, in xe2x80x9cHigh Brightness Saturated Color Shutter Technology,xe2x80x9d SID Symposium, Vol. 27, p.411, 1996 by Sharp and Johnson and xe2x80x9cRetarder Stack Technology for Color Manipulation,xe2x80x9d SID, 1999, by G. D. Sharp and T. R. Brige, a time-sequential three primary color switch having a high response speed and a saturated chromaticity, which combines a polarization retarder stack (PRS) and a fast-switching liquid crystal light valve, is disclosed. The device disclosed in U.S. Pat. No. 5,751,380 was developed by ColorLink, Inc., as a commercial product known as xe2x80x9cColorSwitch xcex1xe2x80x9d. The relevant description can be referred to in xe2x80x9cHigh Throughput Color Switch for Sequential Color Projector,xe2x80x9d SID 2000 Digest, p.96, 2000, by G. B. Sharp, et al.
FIG. 1 illustrates the structure of the color switch disclosed by G. B. Sharp, in which the reference numeral 10 and 20 respectively represent visible light polarizer, the reference numeral 1, 2, 3 respectively represent light valve units of red color, green color and blue color. The red-color light valve unit 1 includes a ferroelectric liquid crystal (FLC) panel 100, a front PRS 11 and a rear PRS 12. The green-color light valve unit 2 includes an FLC panel 200, a front PRS 13 and a rear PRS 14. The blue-color light valve unit 3 includes an FLC panel 300, a front PRS 15 and a rear PRS 16. A time-sequential pulse 400 is respectively connected to the FLC panels 100, 200 and 300 to emit the polarized red light, green light and blue light in sequence.
Refer to FIG. 2, which is relevant prior art disclosed by the inventor and filed as a patent application entitled as xe2x80x9cFIELD SEQUENTIAL COLOR PROJECTION DISPLAYxe2x80x9d, whose application No. is 09/524,051. In this prior art, the dichroic prisms 90xcx9c95 are used for color separation and recombination. The three FLC panels 70, 72 and 74 are controlled by a time-sequential pulse 110 to emit the light beams of red color, green color and blue color in sequence. The switching speed of the field sequential color projection display system can achieve 0.05 msec. Furthermore, there is substantially no energy loss for the light beams of three primary colors since the system is constructed by dielectric interference filters. However, the alignment of this prior-art system is difficult.
The drawback of the above-described prior arts using FLC panels is the limitation of contrast ratio when a light beam passes through the FLC panel. Therefore, in order to overcome the shortcomings of the prior art, it is important to increase the contrast ratio of the light valve, as well as the response speed of the FLC panel.
Accordingly, an object of the present invention is to provide a fast time-sequential color separator that can be fast switched to output various wavelength ranges of lights having high color purity and high contrast ratio.
A full color LCD projector can be constructed by the color separator, a transmissive or reflective fast-response display element such as a liquid crystal light valve, and other elements such as micro-mirrors, etc.
This invention takes advantage of non-absorption of the interference polarizer and large aperture ratio, high contrast ratio and fast response speed of the reflective ferroelectric liquid crystal panel to constitute a three primary color separator. The polarized incident white light is separated into the light beams of three primary colors by the color filters. A time-sequentially-controlled single-pixel reflective FLC panel then sequentially reflects the color light beams to a single panel of FLC display. The frame frequency of the FLC display can be larger than 0.15 MHz. The CIE coordinates of the three primary colors obtained by the color separator of this invention are (x=0.65, y=0.31), (x=0.28, y=0.69) and (x=0.12, y=0.09), respectively.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention bill become apparent to those skilled in the art from this detailed description.